The indirect injection diesel engine has now given way in the market place to more modern direct injection light duty diesel engines for reasons of fuel economy, performance, and low emissions. However, direct injection diesel engines are much more sophisticated than the earlier indirect injection engines and require more precise calibration be maintained in order to maintain their design performance. The injectors, pumps, filters and other components of the fuel delivery system of the engine are vulnerable to having their operation perturbed by fouling from deposits resulting from combustion of fuel.
Direct injection engines may also use a high pressure common rail fuel system. Recent problems have arisen with the use of ultra low sulfur diesel fuels when used in such high pressure common rail fuel systems. By “high pressure” herein is meant those pressures in diesel fuel systems that are equal to or greater than 15,000 psi (greater than or equal to 1000 bar). Such problems are evident by occurrence of sediment in the fuel additive packages, internal injector deposits, and injector sticking. Accordingly, there was a need to discover the source of the deposit and injector problem when operating engines on ultra-low sulfur fuels, i.e., fuels containing about 15 ppm by weight sulfur or less.
In view of the foregoing and other needs, an embodiment of the disclosure provides a diesel fuel additive composition that has a number average molecular weight (Mn) of from about 500 to about 10,000. The additive is selected from a hydrocarbyl-substituted succinic acid or anhydride or derivative thereof, and a hydrocarbyl-substituted Mannich base, wherein the additive has a molecular weight distribution such that less than about 25 wt. % of the additive has a molecular weight of 400 or less as measured by gel permeation chromatography (GPC) based on a polystyrene calibration curve.
In another embodiment of the disclosure provides a method to reduce or prevent injector sticking or deposits in a high pressure common rail diesel engine having injectors and combusting a diesel fuel containing 15 ppm by weight or less sulfur. The method includes combusting in the engine a composition containing the diesel fuel and a diesel fuel additive having a number average molecular weight (Mn) of from about 500 to and 10,000. The additive is selected from a hydrocarbyl-substituted succinic acid or anhydride or derivative thereof, and a hydrocarbyl-substituted Mannich base, wherein the additive has a molecular weight distribution such that less than about 25 wt. % of the additive has a molecular weight of 400 or less as measured by gel permeation chromatography (GPC) based on a polystyrene calibration curve. Use of the fuel containing the additive is effective to reduce the occurrence of injector sticking relative to the occurrence of injector sticking in a comparable engine combusting a fuel containing a similar fuel additive having a molecular weight distribution such that more than 25 wt. % of the additive has a molecular weight of 400 or less as measured by GPC.
Another embodiment of the disclosure provides a method for improving an additive for an ultra-low sulfur diesel fuel in order to reduce deposits and injector sticking in high pressure diesel fuel injection system for a diesel engine. The method includes charging a hydrocarbyl component to a reaction vessel. The hydrocarbyl component is then vacuum distilled at a temperature above about 200° C. for a period of time sufficient to remove at least a portion of the hydrocarbyl components so that a distillation residue of the distilled hydrocarbyl component is effective to provide a diesel fuel additive having a number average molecular weight (Mn) of from about 500 to and 10,000 wherein less than about 25 wt. % of the additive has a molecular weight of 400 or less as measured by gel permeation chromatography (GPC) based on a polystyrene calibration curve. The additive is selected from a hydrocarbyl-substituted succinic acid or anhydride or derivative thereof, and hydrocarbyl-substituted Mannich base. The distillation residue of the hydrocarbyl component is then reacted with a component selected from an unsaturated dicarboxylic acid or anhydride and phenol or substituted phenol to provide a hydrocarbyl-substituted component. The hydrocarbyl-substituted component is then reacted with a reactant selected from an amine and amine plus an aldehyde to provide the additive having a molecular weight distribution of from about 500 to about 10,000, wherein less than 25 wt. % of the additive has a molecular weight of 400 or less as measured by GPC based on a polystyrene calibration curve.
Yet another embodiment of the disclosure provides a method for improving an additive for an ultra-low sulfur diesel fuel in order to reduce deposits and injector sticking in high pressure injection system for a diesel engine. The method includes charging a hydrocarbyl component to a reaction vessel and reacting the hydrocarbyl component with a component selected from an unsaturated dicarboxylic acid or anhydride to provide a hydrocarbyl-substituted component. The hydrocarbyl-substituted component is vacuum distilled at a temperature above about 200° C. for a period of time sufficient to remove at least a portion of the hydrocarbyl-substituted component so that a distillation residue of the distilled hydrocarbyl-substituted component is effective to provide a diesel fuel additive having a number average molecular weight (Mn) of from about 500 to and 10,000, wherein the additive has a molecular weight distribution such that less than about 25 wt. % of the additive has a molecular weight of 400 or less as measured by gel permeation chromatography (GPC) based on a polystyrene calibration curve. The distillation residue of the hydrocarbyl-substituted component is then reacted with a polar compound to provide the additive having a number average molecular weight (Mn) of from about 500 to about 10,000, wherein less than 25 wt. % of the additive has a molecular weight of 400 or less as measured by GPC.
Other embodiments of the disclosure may provide improved stability of a diesel fuel additive package containing a hydrocarbyl-substituted additive wherein less than 25% (by weight) of the additive has a molecular weight of 400 or less as determined by gel permeation chromatography (GPC) based on a polystyrene calibration curve.
Yet other embodiments of the disclosure may provide a method to reduce or prevent visible deposits on the internal parts of a diesel injector in a high pressure common rail diesel engine.
Another embodiment may improve a stability of a diesel fuel additive package containing a hydrocarbyl-substituted additive component by reducing a weight percent of additive precursors having relatively low molecular weight so that the resulting additive has a molecular weight distribution that contains less than 25 wt. % of additive having 400 molecular weight or less as determined by gel-permeation chromatography (GPC) based on a polystyrene calibration curve.
According to one or more embodiments of the disclosure, there may be a significant benefit in improved (reduced) injector sticking occurrence in high pressure common rail diesel fuel systems by reducing or eliminating a percentage of the fuel additive having a low molecular weight, that is, a molecular weight of 400 or less as determined by GPC using a polystyrene standard. It has been surprisingly discovered that deposits formed on injectors are composed primarily of material (lacquers, varnish, salts, etc) containing or derived from such low molecular weight portions of the typical distribution curve of the additive product. In fact, even a small amount, such as 10 wt. %, or 5 wt. % or less of such relatively low molecular weight component in the fuel additive, if present, may result in undesirable deposits, varnish and/or injector sticking. Eliminating or significantly reducing an amount of a relatively low molecular weight fraction of additive from an unmodified distribution curve for such additive, may dramatically improve the engine and injector performance.